The present invention relates, in general, to broadcasting information from a plurality of sources to one or more receivers. More particularly, the present invention is directed to broadcasting a digital information waveform in the same band and on the same channel with a conventional analog waveform.
At present, the sound quality of audio programming over commercial analog frequency modulation (FM) broadcast facilities is significantly poorer than that of more modern digital signal sources such as the compact disc. A number of attempts have been made to bring the quality of digital audio to FM broadcasting, but these attempts have usually given rise to other problems which rendered them unworkable.
For example, U.S. Pat. No. 5,038,402 to Robbins discloses an apparatus and method for broadcasting digital audio over the FM broadcast band and suggests that such digital broadcasts might be interspersed with analog broadcasts, across the band. This patent allows the use of the FM band for digital broadcast, but forces the individual broadcaster to choose between broadcasting in digital, with better audio but a listener base of only the new relatively scarce digital receivers, or conventional analog, with poorer audio quality but available to all listeners with conventional analog FM receivers. The only other alternative is for the broadcaster to broadcast on two frequencies, one for digital and a second for analog; however, this presents a potential problem in obtaining a license for such broadcasting from the Federal Communications Commission (FCC). The broadcaster may or may not be able to acquire a license to broadcast on two frequencies in a given FM radio broadcasting market.
The FCC, in addition to licensing individual frequency bands to individual broadcasters, is charged with allocation of frequency spectrum to all users for all uses. One other problem presented by the system of the Robbins patent and others like it is that spectrum must be allocated especially for digital FM broadcast if the number of analog broadcasters presently on the air is to remain unchanged. This problem is exacerbated by the fact that, for most of the United States and at attainable frequencies, there is no unused spectrum. In order for spectrum to be re-allocated for a new use, the FCC and the petitioners desiring use of a frequency band must go through a protracted, uncertain, political process which will culminate in an FCC decision on how the spectrum in question should be used.
For these reasons, there has been a need for digital audio broadcasting over the FM band which does not require a broadcaster to abandon its investment in analog FM transmission equipment, require a new frequency assignment in the existing FM band, require the listening audience to discard existing analog FM receivers, or force the FM program broadcasters to undergo a protracted, uncertain and expensive process to obtain a new frequency allocation.